Add only unique objects to an array in JavaScript

based on this answer to: "js-remove-an-array-element-by-index-in-javascript"

https://stackoverflow.com/a/7142909/886092

I'm using the following idiom that is concise and does not require underscore.js or any other framework.

Here is an example for recording selected and deselected rows for DataTables jquery plugin. I keep an array of currently selected ids, and I don't want to end up with duplicates in the array:

in coffeescript

  fnRowSelected: (nodes) ->
    position = $selected.indexOf(nodes[0].id)
    unless ~position
      $selected.push nodes[0].id
    return
  fnRowDeselected: (nodes) ->
    position = $selected.indexOf(nodes[0].id)
    if ~position
      $selected.splice(position, 1)

More generally it would

position = myArray.indexOf(myval)
unless ~position
  myArray.push myVal

or in JS

var position;

position = myArray.indexOf(myval);

if (!~position) {
  myArray.push(myVal);
}

The Underscore findWhere function does exactly what you need - it's not an indexOf search by object identity, but searches objects whose properties have the same values as the input.

if (_.findWhere(shippingAddresses, toBeInserted) == null) {
    shippingAddresses.push(toBeInserted);
}

Basic example using lodash union method:

var a = [1,2,3];

// try to add "1" and "4" to the above Array
a = _.union(a, [1, 4]);

console.log(a);

<script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/4.13.1/lodash.min.js"></script>

While this doesn't directly answers the question, it does answers the broader question of how to add unique values to an Array, and like myself, others might stumble upon this page from google.